The comic being posted in the gallery is also from a different set of artists, Krass and Darkneji, as apparent by their signatures... You can find the full comic here:
http://comicsxonline.com/sakuhina-naruto/

I'm not sure this person is aware they are stealing art. It seems more likely that they think of HF as another sharing site, and are posting things they like. I'd chalk it up to a misunderstanding. Would be good to explain to them though.